In the practical application of the Ethernet, various protection techniques are widely used, and implement the redundancy backup between the active path and the standby path. When the active path and the standby path are both in the good condition, the protection data forwarding function of the standby path is blocked, and the protection data between networks are transmitted on the active path; when the fault occurs on the active path, the protection data forwarding function of the standby path is opened, and the protection data between networks are transmitted by switching to the standby path, so as to prevent the protection data from being repeatedly received and forming the broadcast storm, improving the anti-fault capability of the Ethernet, and satisfying the higher real-time requirement that the convergence time is less than 50 ms when switching.
With reference to the Ethernet ring protection technique shown in FIG. 1, nodes A to F are all nodes with the Ethernet switching function, the network M connects with the node B, and the network N connects with the node D. The network M communicates with the network N. There are two physical paths between the network M and the network N, namely the network N <—> the node D <—> the node C <—> the node B <—> the network M, and the network N <—> the node D <—> the node E <—> the node F <—> the node A <—> the node B <—> the network M.
When the Ethernet ring protection technique is applied, the ring protection link and the control node are generally defined, namely in the fault-free case of the Ethernet ring, the link for blocking the data message to prevent the ring from forming on the ring is the ring protection link, and by operating this ring protection link, switching can be performed between the active path and the protection path of the ring network. The node with the ring protection link is called as the control node (or called as the main node) herein. As shown in FIG. 2a, the nodes included in the ring network are A, B, C, D, E, and F, the included links are links <A, B>, <B, C>, <C, D>, <D, E>, <E, F> and <F, A>. The node A is a control node, and the link <F, A> which directly connects with the e port of the node A is the ring protection link.
When the link on the ring is in a good condition, the control node blocks the data message forwarding function of the port connecting with the ring protection link, no ring is generated in the network, and the “broadcast storm” caused by the network ring is prevented. As shown in FIG. 2a, the control node A blocks the protection data forwarding function of the e port, and the communication path of the networks M and N is: the network M <—> the node B <—> the node C <—> the node D <—> the network N.
When the fault occurs in the link, the control node opens the data message forwarding function of the port connecting with the ring protection link, thereby ensuring the connection of the service. As shown in FIG. 2b, a fault occurs in the link <B, C> on the ring, the control node A opens the data message forwarding function of the port e, and the new communication path of networks M and N is: the network M <—> the node B <—> the node A <—> the node F <—> the node E <—> the node D <—> the network N.
Actually, when the network topology changes, the nodes in the ring network should refresh the address forwarding list, which is for the purpose of preventing the data path from still transmitting along the path before the topology changing. For example, in FIG. 2a, the ring network does not have a fault, the communication path between the network M and the network N is the network M <—> the node B <—> the node C <—> the node D <—> the network N. When the fault occurs in the link <B, C> in the ring network, and if the communication path between the network M and network N still forwards along the previous path, data message will be discarded in large amount. At present, the ITU-T G.8032 uses the topology change point to periodically send the address refreshing message to solve the above problem, and the specific scheme of refreshing the address in the single ring is: when the port in the ring network of one node receives protocol message with the refreshing information, this port extracts the <Node_ID, BPR> information from this protocol message, wherein Node_ID is the information of the node which sends this protocol message, the BPR is used for pointing out which port on the ring of the node sending this protocol message is blocked, and the BPR parameter only has the local meaning. This port compares the <Node_ID, BPR> information in the message with the <Node_ID, BPR> information previously stored in this port. If these two are inconsistent, this port deletes the previously stored <Node_ID, BPR>, and stores the new <Node_ID, BPR>. If the newly stored <Node_ID, BPR> is inconsistent with the <Node_ID, BPR> stored in another port of this node on the ring are inconsistent, this node refreshes the address forwarding list, namely, deletes all the forwarding entries in the address forwarding list, and said forwarding entries are the basis for forwarding packets.
The above scheme solves quite well the repeated refreshing problem caused by periodically sending the message with the address refreshing information, namely, the problem of repeatedly refreshing the address forwarding list caused by the subsequent address refreshing message. However, this scheme is unable to completely eliminate the problem of repeatedly refreshing the address. As shown in FIG. 3, the fault occurs in the link <B, C>, the node C sends the SF1 message (the SF1 message includes the <Node_ID(C), e> information) along its w> port, and the node B sends the SF2 message (the SF2 message includes the <Node_ID(C), w> information) along its e port. The e ports of nodes D, E, F and A on the ring detect that the <Node_ID(C), e> in the SF1 is different from all of the <Node_ID, BPR> stored in their e port and w port when receiving the SF1 message for the first time, and refresh the address forwarding list. Similarly, the w ports of nodes D, E, F and A on the ring detect that the <Node_ID(B), w> in the SF2 is different from all of the <Node_ID, BPR> stored in their w port and e port when receiving the SF2 message for the first time, and refresh the address forwarding list. Nodes C, D, E, F, A and B on the ring refresh the address forwarding list twice.
It can be seen from the above example that each topology change on the ring will cause the node on the ring to refresh the address forwarding list twice in the traditional scheme, which will cause that the ring network is difficult to enter into the stable state from the broadcast storm state in short time. Therefore, a new scheme of refreshing the address needs to be promptly proposed.